The present invention relates to the measurement of optical signals, and more particularly to the automatic testing of dense wavelength division multiplexing (DWDM) systems.
A new type of technology has emerged over the last few years in the telecommunications industry. This technology is called dense wavelength-division multiplexing (DWDM) and combines multiple optical channels onto a single optical fiber, each channel transmitting at a slightly different wavelength. This technology thus multiplies the carrying capacity of a single optical fiber by as much as two orders of magnitude. While greatly enabling the transport of large amounts of data over optical fiber, DWDM adds a level of complexity not seen in earlier transmission systems. In the past telecommunications technicians were largely unconcerned about spectral measurements, but with the advent of DWDM such measurements become critical. This has the unintended effect of thrusting the technicians into a mode requiring testing with optical spectrum analyzers (OSAs).
Traditionally optical spectrum analyzers have been large, cumbersome machines with complicated user interfaces designed for specialist engineers. Emphasis was on flexibility and raw performance, in much the same way that early optical time domain reflectometers (OTDRs) were designed primarily for engineers. Today expectations for test equipment have radically changed, and ease of use is a key requirement. This expectation derives from the fact that telecommunications operators have cut back on technician staff. No longer are technicians allowed the luxury of being specialists on one type of equipment. Instead they must be able to competently use many different types of equipment. To do this much of the testing intelligence must now be built into the test equipment. The ideal user interface is one that requires the operator to connect the equipment and push a single button. The results, rather than being just data that the user must interpret, should be in the form of conclusions about the system being tested with higher-level functionality residing behind this simple user interface.
Today technicians want to know if their DWDM optical network is operating within performance specifications. Many would be happy with a simple xe2x80x9cyesxe2x80x9d or xe2x80x9cnoxe2x80x9d answer. To get this answer they must operate the OSA, meaning they must supply acquisition parameters. Next they must interpret a waveform and/or event tables and from that information draw a conclusionxe2x80x94is the system operating within specification or not? Setup parameters may include entering such information as: start/stop wavelengths; center wavelength and span; sensitivity level; saturation level; and resolution bandwidth. Once the waveform is acquired the user often wants to know the answers to the following questions:
How many channels are operating?
Are all channels operating with specification?
Are the channels properly centered in the ITU grid?
Are the channels sufficiently equal in magnitude?
Are any channels below the minimum acceptable power level?
Are any channels above the maximum acceptable power level?
Is the OSNR within specification for each channel?
Is there excessive gain tilt in the system?
Have any channels drifted appreciably in power or frequency since the last test?
As is apparent there is a wealth of information that must be available to the user in order to make these assessments. Furthermore the user needs to have a detailed familiarity with the instrument just to make an acquisition. If the measurements are not made automatically, the user must also have considerable experience in using the instrument in order to get full value out of the measurements made.
What is desired is an OSA for technicians that has a very simple user interface which selects the acquisition parameters and makes a report describing system-level compliance with specifications based on automatic testing of the OSA waveform.
Accordingly the present invention provides automatic testing of DWDM systems that provides a test solution which allows technicians quick access to the most important question: do the spectral characteristics of the DWDM system meet the manufacturer""s specifications. Upon turning on an optical spectrum analyzer (OSA) and connecting it to the DWDM system, the OSA presents the user with the option of manual or automatic testing. Selection of the automatic testing provides a menu listing all the major DWDM systems, the specifications for which supplied by the manufacturers is stored in the OSA""s updatable memory. Selection of the appropriate DWDM system from the menu automatically configures the OSA""s acquisition parameters, initiates a test sequence and generates a report telling the user whether the system is meeting all its specifications and, if not, where the problem is.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.